1. Field of the Invention
The present invention relates generally to the field of telecommunications and, more particularly, to methods for supporting handover of real-time packet data flows within a wireless telecommunications system.
2. Background of the Invention
Wireless data networks are usually composed of a wired, packet-switched, backbone network and one or more wireless (e.g. cellular radio or infrared) hops connecting mobile hosts to the wired part. The wireless part is organized into geographically-defined cells, with a control point called a base station (BS) for each of these cells. The base stations are on the wired network and provide a gateway for communication between the wireless infrastructure and the backbone interconnect. As a mobile host (MH) travels between wireless cells, the task of routing data between the wired network and the MH must be transferred to the new cell""s base station. This process, known as a handoff, must maintain end-to-end connectivity in the dynamically reconfigured network topology.
Network protocols in cellular wireless data networks must update routes as a mobile host moves between cells. As mentioned above, these routing updates combined with some associated state changes are called handoffs. Most current handoff schemes in wireless networks result in data loss or large variations in packet delivery times. Unfortunately, many applications, such as real-time multimedia applications and reliable transport protocols, adapt to long term estimates of end-to-end delay and loss. Violations and rapid fluctuations of these estimates caused by handoff processing often results in degraded performance. For example, loss during handoff adversely affects TCP performance often causing a timeout thus dropping the connection between the TCP client and the host. High packet loss and variable delays result in poor real-time multimedia performance. Furthermore, variable delays often result in gaps or pauses in voice communications.
The current standards working assumptions within GSM/GPRS ETSI groups and 3GPP UMTS groups regarding packet data flows are as follows. Packet data flows are non-real-time. Therefore, handover can be non-real-time. Packet data flows are buffered at the User Equipment (UE) (known as a Mobile Station (MS) in GSM/GPRS) and are also buffered at the SRNS (or SGSN within GPRS). However, the prospect of running voice services (or any other real-time service such as video) over the Packet Domain of UMTS and over the GPRS backbone does exist. When the standards working assumptions are changed to enable these real-time packet data flows, the latency introduced during the currently defined handover procedure is intolerable.
In addition to the current standards working assumption, two variations have been considered. In one variation, the connection with the UE is suspended and resumed as in the standards working assumption. At, the GGSN, the downlink GPRS Tunneling Protocol (GTP) connection is moved to the DRNC (new SRNC) immediately (therefore no buffering is needed at the GGSN). Then, when the SRNC is ready, the suspended connection with the UE is transferred to the DRNC (the new SRNC). Finally, the new downlink GTP tunnel is connected with the transferred UE connection at the DRNC. However, this technique only reduces the xe2x80x9csuspendxe2x80x9d period during the handover (as compared to the standards working assumption). If multiple GGSNs are connected to the UE when the handover is performed (or if multiple QoS levels were being supported simultaneously), then all of these tunnels would have to be moved before the UE connection could be resumed, which would only increase the pause in the communication.
The other variation that is being considered is to suspend and resume the connection with the UE as in the above described variation. However, each GGSN involved forks its downlink GTP tunnel to send packets to both the SRNC and DRNC, thus minimizing the disruption when the DRNC is ready to take over as the new SRNC.
Other solutions describe methods that utilize excessive air interface resources to accomplish a real-time handover. This is undesirable given the scarcity of radio resources. Therefore, a method and system for supporting handover of real-time packet data flows within a wireless telecommunications system such as the Universal Mobile Telecommunications System (UMTS) Packet Domain which provides a very small interruption or no interruption in packet flow is desirable.
The present invention provides a method of controlling handover of real-time packet data flow within a wireless telecommunications system packet domain without disrupting communication between user equipment and the anchor packet gateway. In a preferred embodiment, the wireless telecommunications system includes user equipment such as wireless user equipment, a serving wireless gateway, a drift wireless gateway, and an anchor packet gateway. Once it is determined that handover of real-time packet data flow is needed, the drift wireless gateway is prepared to become the serving wireless gateway. The anchor packet gateway is then prepared for serving wireless gateway relocation by having the anchor packet gateway initiate bicasting of downlink packet data flow. Uplink and downlink packet data flows are then monitored at the drift wireless gateway and the drift wireless gateway and the serving wireless gateway are synchronized for relocation. The drift wireless gateway is then utilized as the new serving wireless gateway.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.